Summary

• persist user-uploaded custom style reference images immediately, independently of AI analysis
• return stable project media preview URLs for custom styles and render them in list/detail views
• show the local image with an analysis spinner, reject unsupported formats, and stop on API error envelopes

Root cause

The upload flow treated an HTTP 200 error envelope as success and continued into analysis/style creation without a valid preview path. Custom style metadata also had no persisted preview path, and generated media URLs used the resolved project name instead of the requested project ID, causing 404 responses in the UI.

User impact

Preset previews remain bundled and read-only. User-uploaded custom style images are stored under the project, survive reloads, and appear in both the style list and detail panel as soon as upload succeeds; AI analysis remains a separate follow-up state.

Verification

• uv run pytest tests/test_api_styles.py -q — 17 passed
• uv run ruff check src/novelvideo/api/routes/styles.py src/novelvideo/services/style_service.py tests/test_api_styles.py
• pnpm exec vitest run src/__tests__/routes/styles.ce.test.tsx — 4 passed
• pnpm build
• Docker Compose against an isolated clone of existing project data: upload/create/list/detail/media/delete all succeeded; media returned 200 image/png

Closes #152